Spektrale aktinische Flussdichten und Photolysefrequenzen – Untersuchungen in der atmosphärischen Grenzschicht und der freien Troposphäre

Lohse, Insa Mareike

Dissertation / PhD Thesis/Book

FZJ-2015-06240

Spektrale aktinische Flussdichten und Photolysefrequenzen – Untersuchungen in der atmosphärischen Grenzschicht und der freien Troposphäre

Lohse, I. M. (Corresponding author)FZJ*

2015
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-086-9

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment 285, VI, 111, VII-XXIII S. (2015) = Universität Köln, Diss., 2015

Please use a persistent id in citations: http://hdl.handle.net/2128/9364

Abstract: Solar UV radiation is driving atmospheric photochemistry because the photolysis of atmospheric trace gases yields highly reactive atoms or radicals. Thus, trace gas concentrations as well as accurate photolysis frequencies are needed to understand atmospheric photochemical processes. Especially under varying cloud conditions, measurements can often not be replaced by radiative transfer calculations with sufficient accuracy. In this work, airborne measurements of the separate upwelling and downwelling components of the actinic flux densities (280–650 nm) were performed with CCD-spectroradiometers. For accurate UV measurements a thorough treatment of stray light was applied for the single monochromator based array spectrometers. Moreover, the angular sensitivities of the optical receivers were determined to analyze their influence under various atmospheric conditions using radiative transfer calculations of realistic atmospheric radiance distributions. Corresponding correction factors in the range of 5% were derived. The overall performance was tested on the ground by in-field comparisons with a doublemonochromator reference system and found to have maximum deviations of 7%. Measurements of the spectral actinic flux density were performed aboard Zeppelin NT in the atmospheric boundary layer during the PEGASOS campaign 2012/13 over different parts of Europe. Moreover the research aircraft HALO was used during the NARVAL campaign 2013/14 for measurements in the upper troposphere and the lower stratosphere over the Atlantic Ocean. Typical Zeppelin flight heights ranged from 100m to 900m and flights were therefore always performed below possible cloud layers. Thus the measurements were influenced by potentially overlaying clouds and a small upwelling part of radiation. Radiative transfer calculations of the downwelling component under the assumption of clearsky conditions showed good agreement with the maximum values of the measurements. The upwelling component of the spectral actinic flux density was unexpectedly greater than the model results. The reason for this is unknown and requires further reasearch. Owing to the typical flight heights of HALO in the range 8–14 km, the measurements were affected by a high upwelling part of radiation, especially when flying over clouds. The measured downwelling components of j(O$^{1}$D) and j(NO$_{2}$) for all flights and various cloud conditions showed only small deviations of 4–5% compared to clearsky model calculations. Cloud-microphysical properties of underlying clouds were retrieved for a certain time period of a HALO-flight using spectral radiance measurements performed by the Leipzig Institute for Meteorology and were used as additional input parameters for radiative transfer calculations of spectral actinic flux densities. The deviations between model and measurements of up to 40% for the upwelling component can partly be attributed to the geometrical receiving characteristics of the radiance optic. Comparisons of measured photolysis frequencies and model values of regional and global chemistry transport models showed good agreements with small underestimations of j(NO$_{2}$) by the models in the range of 20%. For the PEGASOS campaign the regional EURAD-IM model was found to overestimate j(O$^{1}$D) significantly due to a low and constant ozone column in the model. For the NARVAL campaign good agreement for j(O$^{1}$D) with the global MOZART model, that uses variable, modelled ozone columns, was obtained.

Note: Universität Köln, Diss., 2015

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